1. Field of the Invention
The present invention relates to a rectifier unit equipped to a flowmeter that measures a flow volume of fluid, and more particularly to a rectifier unit and a rectifier attaching structure with enhanced rectifier attaching capability.
2. Description of the Related Art
For a rectifier attached to a flowmeter, as is shown in FIG. 12, a flow sensor 124 serving as a flow rate sensor is generally attached to an intermediate portion of a flow channel 123 defined to transversely penetrate through a main body 122 of a flowmeter 121. The flow sensor 124 measures a flow rate produced within the flow channel with the use of a flow chip, and outputs the measurement result in the form of a voltage, on the basis of which a flow volume is measured.
Incidentally, in order to stabilize the measuring ability of the flow sensor 124, rectifiers 125, such as rectifier wire meshes, each rectifying fluid flowing from the upstream side of the flow sensor 124 to a homogeneous flow, are provided at regular intervals with spacers 126 being interposed along a flow channel direction (see, for example, JP-A-2-263117). Further, in order to close the portion of the spacers 126 in a reliable manner and prevent the fluid from leaking, a coupler 128 is attached while a sealing O-ring 127 is interposed at the end face of the flow channel 123 on the lead-in side.
With such a rectifier attaching structure, however, a rectifier and a spacer are alternately inserted one by one in the tube from an opening of a lead-in tube of the flow channel to be pushed sequentially to the deepest portion of the lead-in tube, and this insertion operation has to be repeated as many times as the number of components that need to be attached, which makes the job quite troublesome. In particular, a time needed for the insertion operation is extended as the diameter of the flow channel is reduced with a reduction in size and the rectifiers and the spacers become smaller as well, which lowers the working efficiency and deteriorates the assembling performance. In addition, there is a limit in reducing the size or the number of components due to the need for a coupler to keep the opening side of the spacers closed.
Further, there is a possibility that a rectifier and a spacer are inserted in a wrong order or skipped by mistake. In such a case, the rectifiers are not provided at regular intervals, and the originally expected rectifying function cannot be achieved. Moreover, once the rectifiers are attached inside the lead-in tube, there is no way to confirm whether the rectifiers are attached adequately. In addition, it is impossible to address a need for a change to the specifications regarding the number of rectifiers to be provided, because no adjustment can be made. For example, when a need for a change to the specifications is to reduce the number of rectifiers to be provided from the predetermined regular number, in a space where the rectifiers and the spacers are to be provided, a total length in the channel flow direction becomes shorter by a thickness of the reduced rectifier(s), which gives rise to a clearance equivalent to the reduction. The clearance may possibly cause the leakage of fluid, and it is therefore difficult to add a change to the specifications.